The use of biocompatible long-term implanted shunts has become more prevalent as a treatment modality for a variety of illnesses and diseases.
For example, the development of shunts for the treatment of hydrocephalus was a major advance in neurosurgery. Shunting has such a dramatic effect on the natural history of hydrocephalus that it is the sole treatment used for many causes of hydrocephalus. The placement of a cerebrospinal fluid shunt is now the third most commonly performed neurosurgical procedure in the United States annually and the most common pediatric neurosurgical procedure. Nonetheless, shunts are plagued with the highest complication rate of all neurosurgical procedures.
The one and five year failure rates for CSF shunts have been reported to be between 20-30% and 23-49%, respectively. The most common reason for shunt failure is obstruction of the catheter. Proximal obstruction accounts for nearly half of all failures in most reported series while distal obstruction accounts for up to 35% of obstructions. Blockage of the valve also is a common problem. Some catheters are blocked at multiple sites.
The specific cause of failure for a given catheter appears to be a function of time. The vast majority of infections, valve-problems, or proximal obstructions requiring catheter removal occur within two years of insertion. Catheters that fail after two years are obstructed distally more than two-thirds of the time.
The materials responsible for obstruction are varied. Typically, the proximal catheter is blocked by ingrowth of choroid plexus or glial tissue, or obstructed by blood or cellular debris. Distally, the peritoneum can grow into the catheter and obstruct its lumen.
Neurosurgeons often encounter the problem of shunt failure. In the pediatric myelomeningocele population, one frequently encounters patients who have undergone dozens of shunt revisions. The combined neuropsychological, economic, and psychosocial impact of multiple shunt failures and revisions on the life of a given patient is profound.
A number of inventions have been directed towards preventing the obstruction of hydrocephalus shunts. See e.g., Stati et al., U.S. Pat. No. 3,829,903; Labianca, U.S. Pat. No. 4,375,816; Ahmed, U.S. Pat. No. 5,728,061; Wong et al., U.S. Pat. No. 5,000,731; Schulte et al., U.S. Pat. No. 4,636,194; Corbett, U.S. Pat. No. 4,655,745; Hooven et al., U.S. Pat. No. 4,601,724; Schulte et al., U.S. Pat. No. 4,560,375; Wortman et al., U.S. Pat. No. 3,690,323; and Ames, U.S. Pat. No. 3,452,757. Each of those inventions uses a mechanical means to prevent blockage.
Other inventions use enzymes to prevent obstruction of a catheter lumen. For example, Van Anterwerp, U.S. Pat. No. 5,505,713, describes a process for producing a catheter and a catheter with a stable enzyme coating to prevent and dissolve fibrin or lipid-based obstructions within the lumen of the catheter. The means for attaching the enzymes is a polymer, an encapsulation method or a cross-linked matrix. The attachment means controls the rate of enzyme degradation. However, Van Anterwerp provides for the coating of the external surface of the catheter that is indwelling in the patient, not the lumen interior surface. Accordingly, the catheter and process described in Van Anterwerp is contraindicated for a shunt to be placed in cranial cavity where enzymatic degradation of externally contacting brain matter would be unacceptable.
Various patents to Guire, U.S. Pat. Nos. 3,959,078, 5,263,992 and 5,217,492 describe a system for attaching and stabilizing enzymes in a matrix. However, they do not use a hydrogel or other polymer matrix to bind the enzymes to the catheter and are limited in other important respects, e.g., specifies the use of specific biofunctional agent.
Similarly, Mosher, U.S. Pat. 5,114,413 describes the use of a proteinaceous material to coat the interior of a catheter, but is limited preventing blood components and cellular matter from adhering to the surface and is not directed to precluding the obstruction of the catheter lumen.
Thus, despite numerous and concerted efforts, a cost-efficient method has not been devised to create a biocompatible catheter that precludes shunt obstruction. In particular, despite the long felt need for such method or device in the cerebrospinal shunt industry, until Applicants"" invention, no such method or device existed.
Accordingly, it is an object of this invention to provide a biocompatible catheter that degrades cellular material in the lumen of the catheter. It also is an object of this invention to provide a biocompatible catheter that degrades blood in the lumen of the catheter. It is also an object of the invention to provide a biocompatible catheter that degrades choroid plexus and peritoneum within its lumen. It is a further object of this invention to provide a catheter that degrades omentum within its lumen. It is an object of the present invention to provide a biocompatible catheter that is resistant to obstruction. It is a further object of this invention to provide a long-term placement biocompatible catheter that is resistant to obstruction. It is another object of this invention to provide for a CSF shunt that is resistant to obstruction. Other objects will be readily apparent based on the following detailed description taken with the figures.